Conventional hydrometers for battery fluid comprise a cylindrical rod having fixed specific gravity calibrations enclosed within an enclosure with suction means. When such a device is to be used to measure the specific gravity of battery fluid, a sample of battery fluid is drawn from the battery and the device is placed vertically to read the calibration on the cylindrical rod, however, the readings from the calibration are usually inaccurate. Besides, if the temperature of the measuring fluid is either too high or too low, it is rather difficult to hold the hydrometer vertically with hands in order to read the calibrations. Therefore, conventional hydrometers possess drawbacks which are to be overcome.